AUA 2018: Temperature Elevation During High-Power Holmium Laser Lithotripsy in an In Vivo Porcine Model

San Francisco, CA USA ( Ali Aldoukhi, MD, clinical urologist from the University of Michigan, Ann Arbor, MI, presented his data on the photothermal effect of holmium laser stone fragmentation. Aldoukhi and his team of researchers wanted to determine safe parameters of laser lithotripsy with intraoperative effects within a porcine model. They used previous in vitro studies, which showed that increased temperature to renal tissue does cause injury, as their inspiration to pursue this research question. To carry out this research, the experimenters used two methods of temperature monitoring within a live, anesthetized, non-survival female pig: a needle thermocouple that was inserted from the exterior of the kidney within the calyces and a wire thermocouple that was fed through a ureteroscope. A total of five kidneys were used within their current cohort.

In each trial, a 242 µm laser fiber was introduced to the center of the upper pole calyx and away from the thermocouple. Then, 40 Watts of laser energy was applied for 60 seconds in each trial. Each trial varied in the amount of irrigation that was given within the specific calyx. Thermal dose for each trial was calculated based on previous research conducted by Sapareto and Dewey t43 equivalence calculations from their research publication in 1984. Sapareto and Dewey also determined the safe threshold level of renal injury due to temperature which was 50°C.

Following the collection of data, it was determined that the trial with no irrigation was the most detrimental to the renal anatomy. For the no irrigation trials, it took on average 13 seconds (range 2-37 sec.) for the temperature to reach the threshold of thermal injury. The medium irrigation also reached the threshold of thermal injury on average after 17.8 seconds (range 5-30 sec.). Only the trials with high irrigation never progressed past the threshold of thermal injury. The peak temperatures experienced for the no irrigation, medium, and high irrigation trials were 84.8, 63.9, and 43.6 °C, respectively.

Through this study, the researchers were able to determine that high-power holmium laser energy, ≥ 40 W, can induce injurious temperature elevations in a porcine model. Dr. Aldoukhi explained how a variety of techniques such as greater irrigation flow, intermittent laser activation, and even cooled irrigation fluid may be used to mitigate thermal effects during laser lithotripsy utilizing these high energy levels.

Presented by: Ali Aldoukhi

Written by: Zachary Valley, Department of Urology, University of California-Irvine at the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA